1. Field of the Invention
The present invention relates generally to methods and apparatus for mixing chemicals used in semiconductor manufacturing processes and, more particularly, to methods and apparatus for mixing chemicals for use in chemical mechanical polishing processes.
2. Description of the Related Art
Chemical mechanical polishing (CMP) planarization techniques are commonly used in the manufacture of layered semiconductor devices. In typical CMP processes, a workpiece or wafer to be polished is pressed against a polishing pad under controlled conditions in the presence of a chemical mixture. The chemical mixture typically comprises a slurry including small, abrasive particles that abrade the surface of the wafer, and chemicals that etch and/or oxidize the surface of the wafer. When the pad and the wafer are moved with respect to one another, material is chemically and mechanically removed from the surface of the wafer to produce a polished or planarized surface.
Chemical mixtures used in CMP processes vary depending on the material to be removed from the surface of the wafer. If a metal surface is to be polished, the mixture may comprise, for example, a slurry containing a suspension of electrically charged alumina or silica particles and an oxidizer comprising, for example, hydrogen peroxide. If a nonmetal surface is to be polished, the mixture may comprise, for example, a slurry containing a suspension of electrically charged silica particles and, for example, ammonia or ammonium hydroxide.
In order to ensure consistent process results between wafers, it is necessary to precisely control the composition of the chemical mixture used. Prior art CMP systems typically include volumetric pumps that pump the various components of the mixture from bulk sources to a mix chamber where the components are mixed together. While typically providing high throughput, such systems typically do not allow precise control of the mixture composition due to the limited precision of the volumetric pumps. Accordingly, a need exists for a CMP system in which the composition of the chemical mixture delivered to the wafer can be precisely controlled without adversely affecting throughput.
In accordance with one aspect of the present invention, a method of preparing a fluid mixture comprising predetermined amounts of two or more fluids is provided. The method comprises the steps of providing a first vessel having a body and a neck extending upwardly from the body. The neck has a smaller cross-sectional area than the body. A first fluid is delivered to the first vessel to fill the body and at least a portion of the neck. A sight tube indicating an amount of the first fluid in the first vessel is read, preferably by an optical sensor. The delivery of the first fluid is discontinued when the sight tube indicates that a predetermined amount of the first fluid is in the first vessel. A second vessel is also provided. A second fluid is delivered to the second vessel. A sight tube indicating an amount of the second fluid in the second vessel is read, also preferably by an optical sensor. The delivery of the second fluid is discontinued when the sight tube indicates that a predetermined amount of the second fluid is in the second vessel. The predetermined amounts of the first and second fluids are then delivered to a mix chamber and mixed.
In accordance with another aspect of the present invention, a chemical delivery apparatus is provided, comprising a first vessel having a body and a neck extending upwardly from the body. The neck has a smaller cross-sectional area than the body. A fluid inlet is provided near a top of the neck. A fluid outlet is provided near a bottom of the body. A first sight tube port is provided near the top of the neck, and a second sight tube port is provided near the bottom of the body. A sight tube is connected between the first and second sight tube ports to indicate an amount of fluid in the first vessel. A first fluid source selectively communicates with the first vessel through the fluid inlet of the first vessel. A second vessel is also provided, comprising a fluid inlet and a fluid outlet. A second fluid source selectively communicates with the second vessel through the fluid inlet of the second vessel. A mix chamber selectively communicates with the first and second vessels through the fluid outlets of the first and second vessels.
In accordance with another aspect of the present invention, a method of preparing a fluid mixture comprising predetermined amounts of two or more fluids is provided. The method comprises the steps of providing a vessel having a body and a neck extending downwardly from the body. The neck has a smaller cross-sectional area than the body. A first fluid is delivered to the vessel to fill a portion of the neck. A sight tube indicating an amount of the fluid in the vessel is read, preferably by an optical sensor. The delivery of the first fluid is discontinued when the sight tube indicates that a predetermined amount of the first fluid is in the vessel. A second fluid is then delivered to the vessel to fill a remaining portion of the neck and at least a portion of the body. The sight tube is read by the optical sensor, and the delivery of the second fluid is discontinued when the sight tube indicates that a predetermined amount of the second fluid is in the vessel. The predetermined amounts of the first and second fluids are then delivered to a storage chamber.
In accordance with another aspect of the present invention, a chemical delivery apparatus is provided, comprising a vessel having a body and a neck extending downwardly from the body. The neck has a smaller cross-sectional area than the body. First and second fluid inlets are provided near a top of the body. A fluid outlet is provided near a bottom of the neck. A first sight tube port is provided near the top of body, and a second sight tube port is provided near the bottom of the neck. A first fluid source selectively communicates with the vessel through the first fluid inlet. A second fluid source selectively communicates with the vessel through the second fluid inlet. A sight tube connected between the first and second sight tube ports indicates an amount of fluid in the vessel. A storage chamber selectively communicates with the vessel through the fluid outlet.